Paper and a method of making paper

ABSTRACT

Paper is formed from typically cellulose fibres which have a tendency to become discoloured during processing. Thus, in order to provide good quality white paper, it is necessary to bleach that paper to limit biological activity and remove discolouration. Of concern with respect to this particular invention is also the requirement to add so-called optical brightness agents (OBA). These optical brightness agents essentially fluoresce in daylight in order to give the impression of pure white colour even though the underlying fibres are still yellow white after bleaching. Optical brightness agents are expensive and therefore the present invention provides a composition which reduces the proportion of OBA agent necessary to achieve desired base point increases in paper quality. The composition comprises peroxyacetic acid or peracetic acid and hydrogen peroxide in the relative proportions whereby the fibre surface is processed in order to be more receptive to the activities of OBA and therefore, provide greater paper quality improvement relative to the relative volume of OBA added.

[0001] The present invention relates to paper and methods of makingpaper and more particularly, to compositions, pulp suspensions andprocessing to provide for white paper production.

[0002] Paper is made from a pulp stock or suspension incorporating anumber of ingredients but principally fibres in order to provide throughappropriate processing sheets or rolls of paper. The fibres in the paperstock can be obtained from a number of sources but are principallyobtained from tree sources such as cellulose fibre. The tree fibres areappropriately macerated in order to provide the fibres required.Unfortunately, fibres are biologically active and inherently slightlymis-coloured such that in attempting to form good quality white paper itis necessary to bleach that paper. It is also a typical requirement toadd a so-called optical brightness agent (OBA) which is an ultra-violetdye which upon exposure to light radiates a bright white light huegiving the impression of a pure white colour and masks any potentialyellow white in the fibres after bleaching. Unfortunately, OBA materialsare relatively expensive and so care must be taken with the proportionof such OBA material added to the pulp stock for economic reasons. Itwill also be understood that the production of paper inherentlygenerates large volumes of waste water and any contamination and inparticular toxic or environmentally impacting agents such as OBA shouldbe limited in that waste water.

[0003] There are a number of OBA and FWA additives available fromsuppliers such as Bayer AG and from Ciba under their product namesTinopal VP, ABPZ and SPP. Generally, the OBA and FWA additives arefluorescent dyes. Typically, these fluorescent dyes include sulphonatedstilbeane molecules.

[0004] Previous additives to thick pulp stock include sodiumhypochlorite (bleach) and chlorine. Hypochlorite bleaches the fibres inthe pulp stock but the pH level dramatically increases and somebi-products of the bleaching process are deemed environmentallyunfriendly. Furthermore, sodium hypochlorite is a slow acting additiveat low temperatures and residuals from the bleaching process may haveadverse effects on other paper making additives.

[0005] Hydrogen peroxide is also used for bleaching paper stock butnormally at elevated temperatures and with the hydrogen peroxide in aconcentration of at least 50% in the stock. In such circumstances,hydrogen peroxide bleaching of paper stock is very hazardous. It is alsoknown to provide hydrogen peroxide in combination with polydadmac inorder to act as a bleaching agent. However, such a combination onlyprovides a limited increase in paper stock brightness.

[0006] Hydrogen sulphite can also be added to paper stock and is areductive “bleach” in comparison with the sodium hypochlorite andhydrogen peroxide oxidising bleach process. Hydrogen sulphite isgenerally supplied as a powder requiring on-site preparation bydissolving the powder to form the additive solution. If wetted,hydrosulphite releases sulphur dioxide gas with potential dangerousconsequences. Hydrosulphite is also difficult to handle as a liquid andmust be kept dry in order to avoid the sulphur dioxide gas releaseproblem.

[0007] In view of the above, it will be appreciated that currentadditives to bleach paper stock are inconvenient or even dangerous touse whilst they have limited effect upon the brightness achieved or theproportion of fluorescent whitening agent (FWA) or, more commonly,optical brightening agent (OBA) which is required to achieve the desiredpaper brightness and tone.

[0008] In accordance with the present invention there is provided acomposition for cellulose suspensions, the composition comprisingperoxyacetic acid or peracetic acid and hydrogen peroxide in sufficientrelative concentration to reduce the necessary proportion of fluorescentwhiting agent (FWA) or optical brightening agent (OBA) required toachieve the desired brightness in finished paper or paper board productsformed from the cellulose suspension.

[0009] Alternatively, in accordance with the present invention there isprovided a suspension for paper or paper board making, the suspensionincluding an additive comprising a peroxyacetic and/or peracetic acidand hydrogen peroxide composition added to a cellulose fibre stock afterpulping.

[0010] Preferably, the composition comprises at least 12.5 weightpercent peroxyacetic acid and/or peracetic acid. Preferably, thecomposition includes a polyamine or other cationic materials tofacilitate reaction of the peroxyacetic acid and/or peracetic acid withcellulose fibres. Typically, the composition comprises 15% peroxyaceticacid and 14% hydrogen peroxide. Typically, the polyamine or othercationic materials are added in the range of 1-20% by volume to thecomposition.

[0011] Further in accordance with the present invention there isprovided a process for preparing a suspension comprising forming acellulose fibre pulp suspension and adding a composition of peroxyaceticacid and/or peracetic acid and hydrogen peroxide before any otheradditives are added to the suspension.

[0012] Typically, a polyamine or other cationic material is added in therange of 1-20% by volume to the composition in the suspension.

[0013] Preferably, the composition is added in the process when the pulpsuspension has a consistency of at least 2% or greater of cellulosefibres. Typically, if the composition has a concentration of at least12.5% peroxyacetic acid or peracetic acid, then the composition is addedto the suspension in the proportion 50 millilitres of composition pergross tonne of cellulose fibre or dry solids in the suspension.Alternately, there is preferably 7 litres of composition to 1 tonne ofpulp suspension formed from cellulose fibres and water. Furtheralternatively, in the order of 50 g to 7 kg of composition per tonne ofgross paper is initially added then allowed to react for apre-determined process time and a further 50 g to 7 kg of compositionadded per tonne of gross paper for final preparation.

[0014] Typically, the process allows for a process time of at least 30minutes between adding the composition to the pulp suspension and addingany further additives such as FWA or OBA.

[0015] Typically, a polyamine or other cationic material is added in therange of 1-20% by volume to the composition during the process.

[0016] Possibly, the process provides for batch processing of vats ofpulp suspension or continuous processing.

[0017] Typically, pulp suspension is calibrated at the end of theprocess time to determine whether the composition has been effectiveagainst a desired brightness and further composition added, if required,and/or a further period of processing time allowed. Generally, FWA andOBA is added to the pulp suspension at the end of the processing time orat least prior to paper or paper board forming from the pulp suspension.

[0018] Embodiments of the present invention will now be described by wayof example only.

[0019] The process for forming paper is well known. Typically, fibrousmaterials, chiefly of a vegetable origin are mixed with a large quantityof water and shredded into very fine fibres. The suspension or pulpstock typically includes additives such as size, OBA and filler in orderto render a special property to the paper.

[0020] The fibrous material is generally obtained from trees, grasses,bamboo and cotton. There are numerous mechanical, chemical andbiochemical processes for pulping the fibrous material to anappropriately thick stock or stuff for paper or paper board formation.Various grades of paper are provided and typically comprise variouscombinations of fibrous vegetable material as described previously alongwith other fibres such as hemp, linen, wool, asbestos, slag wool, glassfibres and synthetic fibres along with fillers, size and other additivesin order to achieve a desired paper quality.

[0021] The present invention principally relates to providing relativelyhigh quality white paper and paper board. To achieve such high qualitypaper a so-called fluorescent whitening agent or FWA is added. Suchfluorescent whitening agents are also known as optical brighteningagents (OBA). In short, such FWA or OBA materials fluoresce on exposureto light in order that the paper incorporating such agents appearsbrighter and therefore whiter. FWA and OBA are relatively expensiveadditives in a typical paper combination and so there are strongeconomic reasons for limiting their proportion of the combination interms of a weight percentage. It will also be understood that FWA or OBAmaterials are considered unfriendly environmental agents such that wastewater from the paper making process must be appropriately treated toremove such FWA or OBA agents prior to release.

[0022] As with all vegetable matter the fibres used with regard to papermaking will tend to be discoloured relative to the desired whiteness aswell as biologically active. In such circumstances, as indicatedpreviously, it is known to bleach suspensions or pulp stock in order torender the fibres of a whiter surface complexion as well as reducebiological activity which may itself discolour the fibres as the paperages. Traditional bleaching methods, whether they be oxidising orreducing, create their own inherent problems with respect to residualsleft in the paper after forming, processing dangers and waste watercontamination.

[0023] The present invention utilises a composition added to the pulpsuspension prior to other additives. This composition comprises amixture of peroxyacetic acid or peracetic acid with hydrogen peroxide.One source of such composition is Crosmill Limited of Crosmill House,Dragons Lane, Moston, Sandbach, Cheshire, United Kingdom under theirproduct name. Crosmill Millcide PH120 which comprises a solutionincluding 15% peroxyacetic acid or peracetic acid with a similarproportion of hydrogen peroxide. With such a composition, it has beenfound that above a greater than 2.5 weight percent concentration in thepulp suspension the composition provides a sufficiently activeconcentration to render the fibres and more particularly the suspensionstock more receptive to FWA or OBW additives later. Typically, the pulpsuspension or stock will have a so-called thick consistency of upwardsof 2 weight percent cellulose solids or fibres in the suspension.Generally, the composition must be given an effective free period ofprocess time during which it can actively process the suspension. Withthe composition concentration of peroxyacetic acid with hydrogenperoxide described above it has been found that a process time of 30minutes from addition of the composition to the suspension pulp isnormally appropriate. The composition and in particular the peroxyaceticacid and/or peracetic acid conditions the cellulose fibre surface torender it more receptive to association with the FWA or OBA materiallater.

[0024] Clearly, it is still normally necessary to add FWA or OBAmaterials to the suspension stock to achieve the desired whiteness ineventual paper or paper board product. Nevertheless, with the suspensionstock processed in accordance with the present invention, the fibres andthe suspension are more receptive to such FWA or OBA materials and asignificantly lower proportion of such FWA or OBA materials is requiredto achieve the desired brightness in the finished product. Normally, thepresent composition used in the pulp suspension and paper making processwill halve the necessary amount of FWA or OBA which needs to be added toachieve a desired whiteness and brightness.

[0025] As indicated, in order to be effective, the proportion of fibresolids in the suspension should be at least 2% by weight such that thecomposition in accordance with the present invention is able toefficiently process these fibres. A more diluted consistency will renderthe amount of composition which is required to be effective in thesuspension to be significantly increased due to inherent reduction infibre to composition association. The composition in accordance with thepresent invention itself will be relatively costly and therefore themore composition required to process the pulp suspension the less costeffective the process will be. Although excess composition may berecovered from waste water during later stages of the paper makingprocess, such recovery may be expensive and inherently some compositewill be lost through each use cycle.

[0026] As the present composition acts upon the thick suspension ofcellulose fibres used, in accordance with known techniques for papermaking and paper board making, it will be understood that the fibresthemselves will have an increased whiteness or brightness. In somecircumstances, it may not be necessary to add FWA or OBA materials toachieve the desired brightness in the finished paper or paper boardproduct, particularly if white fillers or additives such as chalk,gypsum or china clay are included.

[0027] In accordance with an example of the process of the presentinvention, a suspension pulp will be formed in accordance withconventional techniques to a consistency of at least 2% by weight ofcellulose fibres, a composition of at least 12.5% peroxyacetic acid withproportionate amount of hydrogen peroxide in a liquid form will then beadded in the proportion of 50 millilitres of such composition to eachgross metric tonne of cellulose fibres/solids or 7 litres of compositionper metric tonne of pulp suspension. Typically, individual vats ofsuspension pulp will be processed such that the appropriate processtime, normally 30 minutes, can be applied to each vat of pulp suspensionin accordance with the present invention. Alternatively, throughappropriate pipework and/or holding tanks the suspension pulp can becontinuously processed such that the pulp is at least solely exposed tothe composition for the necessary process time in accordance with thepresent invention between additional of the composition to thesuspension and addition of any further additives to that suspension.

[0028] In order to further improve performance but possibly with theincreased cost and recovery problems, the proportion of composition maybe raised such that composition is added to the suspension pulp with aproportion in the range of 50 g to 7 kg of composition per tonne ofgross paper. The suspension pulp is then allowed to act during a processtime period and then a further volume of composition added in the rangeof 50 g to 7 kg per tonne of gross paper. In such circumstances, thereis a significant increase in brightness lift to the eventual paperquality. For example, if previously there was a one point base paperbrightness lift then by these additions, the brightness lift isincreased to two points in base brightness lift.

[0029] In order to further enhance the process in accordance with thepresent invention, the polyamine or other cationic material can be addedto the peracetic acid or composition. The polyamide or other cationicmaterial will be added in the range of 1-20% by volume to thecomposition in order to further promote the reaction processes performedby the composition in order to prepare the paper pulp suspension forreceipt of an optical brightness agent (OBA). In such circumstances, theproportional improvement in optical brightness relative the amount ofOBA added is significantly increased. Thus, better quality paper can beproduced at a reduced cost or paper quality maintained with lower OBAcontent.

[0030] At the end of the composition processing time, it is found thatthe effect of the composition on the suspension will be to increase thebrightness of that pulp and the resultant finished paper is brighterthan if the composition had not been added. Generally, there is anincreased brightness in the range of 1 to 3 points dependent upon thetype of fibre and initial brightness of the pulp. This increasedbrightness is substantially and proportionately the same with or withoutthe eventual addition of FWA or OBA materials in the finished paper inaccordance with normal practice. There is also a corresponding increasein the whiteness and “L” values of the suspension pulp or finished papersheet. The “L” value relating to brightness within 100=pure white and0=black. The colour of the suspension pulp/finished paper also changes.Typically, the finished paper becomes less yellow and bluer, the “b”value is ratio between blue and yellow and is less positive; this is anadvantage as less dye material may be needed with significant economicsavings whilst promoting improved brightness in the paper itself. The“a” value (red to green ratio) of the finished paper sheet does notchange very much; if there is any change in this “a” value it is a shiftfrom green to red but is normally only of a slight nature.

[0031] As indicated above, after the processed time other additives willnormally be incorporated into the suspension pulp prior to final paperforming and processing. Generally, before such further additives areincorporated into the suspension pulp there will be a calibration testin order to determine the specific whiteness, brightness and othercontrol values used to determine pulp suspension quality. It will beunderstood that as with all natural products, vegetable fibres and inparticular cellulose solids and fibres obtained from tree matter willvary with environment, age, season and source. Thus, the presentcomposition may have significantly different, or at least marginallydifferent, effects upon different batches of suspension pulp. Thus, ifthe “processed” suspension pulp has not met the desired brightness orwhiteness values for onward processing then further FWA or OBA materialsmay be needed or the particular batch of suspension pulp allowed toresume further processing by the composition or, if necessary, furthercomposition added to the suspension pulp to increase the concentrationof the composition in that suspension. In any event, it will beunderstood that temperature along with other factors such as agitationwill significantly effect the necessary processing time to achieve thedesired brightness or whiteness in the suspension pulp and subsequentfinished paper product. Operational temperatures will be in the range 5to 50° C. but the colder temperature the longer time necessaryprocessing time for reaction.

[0032] The present composition and resultant suspension pulp and processallow a paper manufacturer to either maintain finished sheet brightnessand colour at a low cost due to less dye and FWA materials added ormaintain current dye and FWA material content in the finished papersheet but produce a higher quality product with higher whiteness andbrightness. Furthermore, a paper manufacturer could specify a higherquality paper by use of the present composition whilst at the same time,reducing cost through lower dye and FWA additive components specifiedfor that paper.

[0033] It will be appreciated that the present composition effectivelychemically conditions the pulp suspension. Thus, in order to increaseand facilitate the operational efficiency cationic materials may beadded to the composition or separately during the process. The freeradicals provided by disassociation of such cationic material willpromote processing of the suspension pulp by the composition either interms of rate or effectiveness. It will be understood that care will benecessary with regard to the choice of cationic material used such thatthe cationic material is either dissolved in the water or compositionand there is little residual solid cationic material retained in thefinished paper with a potential reduction in the quality of that paper.

[0034] Whilst endeavouring in the foregoing specification to drawattention to those features of the invention believed to be ofparticular importance it should be understood that the Applicant claimsprotection in respect of any patentable feature or combination offeatures hereinbefore referred to whether or not particular emphasis hasbeen placed thereon.

1. A composition for cellulose suspensions, the composition comprisingperoxyacetic acid or peracetic acid and hydrogen peroxide in sufficientrelative concentration to reduce the necessary proportion of fluorescentwhiting agent (FWA) or optical brightening agent (OBA) required toachieve the desired brightness in finished paper or paper board productsformed from the cellulose suspension.
 2. A composition as claimed inclaim 1, wherein the composition comprises at least 12.5 weight percentperoxyacetic acid and/or peracetic acid.
 3. A composition as claimed inclaim 1, wherein the composition includes a polyamine or other cationicmaterials to facilitate reaction of the peroxyacetic acid and/orperacetic acid with cellulose fibres.
 4. A composition as claimed inclaim 3, wherein the polyamine or other cationic material is added tothe composition in the range 1-20% by volume.
 5. A composition asclaimed in claim 1, wherein the composition comprises 15% peroxyaceticacid and 14% hydrogen peroxide.
 6. A suspension for paper or paper boardmaking, the suspension including an additive comprising a peroxyaceticand/or peracetic acid and hydrogen peroxide composition added to acellulose fibre stock after pulping.
 7. A suspension as claimed in claim6, wherein the composition comprises at least 12.5 weight percentperoxyacetic acid and/or peracetic acid.
 8. A suspension as claimed inclaim 6, wherein the composition includes a polyamine or other cationicmaterial to facilitate reaction of the peroxyacetic acid and/orperacetic acid with cellulose fibres.
 9. A suspension as claimed inclaim 8, wherein the polyamine or other cationic material is added tothe composition in the range 1-20% by volume.
 10. A suspension asclaimed in claim 6, wherein the composition comprises 15% peroxyaceticacid and 14% hydrogen peroxide.
 11. A process for preparing a suspensioncomprising forming a cellulose fibre pulp suspension and adding acomposition of peroxyacetic acid and/or peracetic acid and hydrogenperoxide before any other additives are added to the suspension.
 12. Aprocess as claimed in claim 11, wherein the composition is added in theprocess when the pulp suspension has a consistency of at least 2% orgreater of cellulose fibres.
 13. A process as claimed in claim 11,wherein if the composition has a concentration of at least 12.5%peroxyacetic acid or peracetic acid, then the composition is added tothe suspension in the proportion fifty millilitres of composition pergross tonne of cellulose fibre or dry solids in the suspension.
 14. Aprocess as claimed in claim 11, wherein seven litres of composition isadded to 1 tonne of pulp suspension formed from cellulose fibres andwater.
 15. A process as claimed in claim 11, wherein the process allowsfor a process time of at least 30 minutes between adding the compositionto the pulp suspension and adding any further additives such as FWA orOBA.
 16. A process as claimed in claim 11, wherein the process providesfor batch processing of vats of pulp suspension or continuousprocessing.
 17. A process as claimed in claim 11, wherein the pulpsuspension is calibrated at the end of a process time to determinewhether the composition has been effective against a desired brightnessand further composition added, if required, and/or a further period ofprocessing time allowed.
 18. A process as claimed in claim 17, whereinFWA and OBA is added to the pulp suspension at the end of the processingtime or at least prior to paper or paper board forming from the pulpsuspension.
 19. A process as claimed in claim 11, wherein a polyamine orother cationic materials are added to the composition in the proportion1-20% by volume of the composition.
 20. A process as claimed in claim11, wherein in the order of 50 g to 7 kg of composition per gross tonneof paper in initially added then allowed to react for a pre-determinedprocess of time and a further 50 g to 7 kg of composition added pertonne of gross paper.
 21. Any novel subject matter or combinationincluding novel subject matter disclosed herein, whether or not withinthe scope of or relating to the same invention as any of the precedingclaims.